New Thinking: Saturn's Rings Might Be Ancient

Saturn's icy rings shine in scattered sunlight in this view taken by the Cassini spacecraft wide-angle camera on July 4, 2008 at a distance of approximately 1.2 million kilometers (770,000 miles) from Saturn.Credit: NASA/JPL/Space Science Institute

Saturn's rings may be much older and more massive than previously
thought, according to a new study.

The study's computer simulation showed how the
planet's rings could date back billions of years ago to the early ages of
the solar system, rather than only 100 million years ago (during Earth's Age of
Dinosaurs), as previous observations suggested. The calculations are consistent
with recent observations of the rings by the Cassini?Huygensspacecraft
currently studying Saturn and its moons.

Larry Esposito and Joshua Elliott, both at the
University of Colorado, modeled how meteorites smash into the rings, shattering
the ring particles and coating each one in a layer of ice and dust. Before,
scientists had assumed that this shattering led to the eventual dissipation
of the rings, but a new simulation, created by Glen Stewart and Stuart
Robbins of the University of Colorado, shows that after breaking up, the
particles could again clump together in a perpetual recycling process.

Previously, researchers had thought the rings were relatively
young because they appeared bright and pristine, not covered with the detritus
of billions of years of meteorites smashing into them. But the new calculations
show that if the effect of this clumping and re-clumping is taken into account,
the dust would also be recycled through the rings and wouldn't appear as dark
as might be expected.

Many scientists had assumed that we just happened to be
catching Saturn at a relatively rare time when it had rings. Now it would seem
Saturn, and maybe lots of other large planets in the universe also, could have
rings for much of their lives.

"Both Cassini
observations and theoretical calculations can allow the rings of Saturn to
be billions of years old," said Esposito, principal investigator of
Cassini's Ultraviolet Imaging Spectrograph (UVIS) instrument. "This means
we humans are not just lucky to see rings around Saturn. This would lead us to
expect massive rings also to surround giant planets circling other stars."

Our own Jupiter,
Uranus and Neptune each have rings, and even
Earth might have had them once.

Earlier estimates of Saturn?s rings' mass had come from
observations of how much starlight is blocked by the rings. But the new
calculations indicate that these measurements underestimate the mass by about a
factor of three, since they do not account for the clumping effect.

If the rings are really more massive than thought, that
could also help explain why the rings appear so bright and clean. The more
individual pieces of mass in the rings, the more material there is to spread
the pollution around, so the less noticeable it would be to outside
observations.

Esposito will present these findings at the European
Planetary Science Congress in Muenster, Germany, on Sept. 23. Cassini?Huygens
is a joint project by NASA, the European Space Agency, and Italian Space
Agency.